1. Technical Field
Technical field relates to a substrate structure applied in flexible devices.
2. Description of the Related Art
The flexible display is a display that is, like paper, bendable and rollable using a flexible substrate. As it is using plastic materials and films for substrates, it is not only lighter and thinner but also unbreakable upon impact, the flexible display is considered for mobile devices, such as a digital camera, a personal digital assistant (PDA), a smart phone, or a tablet. One of the technologies required for manufacturing flexible devices is the technology that forms the TFT (thin film transistor) array and/or display mediums on flexible substrates.
Fabrication processes are divided into batch type and roll to roll. A TFT apparatus can utilize batch type processes. However, development of substrate-transfer and film-separation techniques is required. The flexible display devices must be transferred to other plastic substrates from glass substrate. For flexible display devices using roll to roll fabrication processes, new equipment is required and some problems caused by rolling and contact must be overcome.
The batch type process is generally categorized into three: the laminated plastic, the transfer to plastic, and the coating plastic. A polyethersulfone (PES) substrate is attached on a carrier plate using the adhesives which can be delaminated by temperature or UV light control. A transmissive type plastic TFT-LCD is developed under that both the processes of TFT and color filter are carried out below 150° C. on PES plastic films. In this manner, a transparent plastic substrate with heat-resistance, a low thermal expansion coefficient and chemical stability is required, and reliable method for bonding preformed plastic substrate to glass substrate before MT processing and then releasing them after TFT processing is necessary.
A low temperature poly-silicon (LIPS) TFT arrays are made on amorphous silicon and silicon dioxide layers on glass. The top of the TFT array is then stuck to a first plastic substrate with water-soluble glue and the TFT layers are freed from the bottom substrate by using a XeCl laser to irradiate the bottom a-Si layer through the glass. The laser beam causes hydrogen exodiffusion, and the released hydrogen lifts the TFTs from the original glass substrate. Then, a second plastic substrate is laminated to the bottom of the TFT array using a permanent adhesive. The array is then released from the first plastic substrate by dissolving the water-soluble glue. This is a double transfer process.
A polyimide layer is applied to a glass substrate by spin coating before TFT array fabrication. The polyimide layer will ultimately become the plastic substrate of the flexible display device. This approach shows that manufacturing can be carried out in well-established factories using existing processes. However, this method also requires a laser beam incident through the back of the glass to decouple the polyimide layer from the glass substrate.